//用javascript实现Base64编码/解码

var keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
//加密
function base64encode(Str) {
    Str = escape(Str);
    var output = "";
    var chr1, chr2, chr3 = "";
    var enc1, enc2, enc3, enc4 = "";
    var i = 0;
    do {
        chr1 = Str.charCodeAt(i++);
        chr2 = Str.charCodeAt(i++);
        chr3 = Str.charCodeAt(i++);
        enc1 = chr1 >> 2;
        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
        enc4 = chr3 & 63;
        if (isNaN(chr2)) {enc3 = enc4 = 64;} else if (isNaN(chr3)) {enc4 = 64;}
        output = output + keyStr.charAt(enc1) + keyStr.charAt(enc2) + keyStr.charAt(enc3) + keyStr.charAt(enc4);
        chr1 = chr2 = chr3 = "";
        enc1 = enc2 = enc3 = enc4 = "";
    } while (i < Str.length);
    return output;
}
//解密
function base64decode(Str) {
    var output = "";
    var chr1, chr2, chr3 = "";
    var enc1, enc2, enc3, enc4 = "";
    var i = 0;
    var base64test = /[^A-Za-z0-9\+\/\=]/g;
    if (base64test.exec(Str)){}
    Str = Str.replace(/[^A-Za-z0-9\+\/\=]/g, "");
    do {
        enc1 = keyStr.indexOf(Str.charAt(i++));
        enc2 = keyStr.indexOf(Str.charAt(i++));
        enc3 = keyStr.indexOf(Str.charAt(i++));
        enc4 = keyStr.indexOf(Str.charAt(i++));
        chr1 = (enc1 << 2) | (enc2 >> 4);
        chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
        chr3 = ((enc3 & 3) << 6) | enc4;
        output = output + String.fromCharCode(chr1);
        if (enc3 != 64) {output = output + String.fromCharCode(chr2);}
        if (enc4 != 64) {output = output + String.fromCharCode(chr3);}
        chr1 = chr2 = chr3 = "";
        enc1 = enc2 = enc3 = enc4 = "";
    } while (i < Str.length);
    return unescape(output);
}

//e.g.
//document.write(base64encode('蓝雨'));
//document.write(base64decode('JXU4NEREJXU5NkU4'));
//document.write(base64decode(base64encode('蓝雨')));
